Defrosting indicator for mechanical refrigerators



1935- J. J. SCHWEITZER 2,007,409

DEFROSTING INDICATOR FOR MECHANICAL REFRIGERATORS Filed Oct. 28, 1952 2 Sheets-Sheet 1 M l'l'l JOHN J1 SCHWE/TZER.

abhor/M y 1935- J. J. SCHWEITZER 2,007,409

DEFROSTING INDICATOR FOR MECHANICAL REFRIGERATORS Filed Oct. 28, 1932 2 SheetsSheet 2 v an extension which is Patented July 9, 1935 UNITED STATES PATENT OFFICE John J. Schweitzer, Sandusky, Ohio Application October 28, 1932, Serial No.

21 Claims. (Cl. 177-311) The proper and economical use of mechanical refrigerators necessitates from time to time the defrosting of the cooling unit thereof, which is length of time, until the ice on the cooling unit has melted off.

This defrosting operation is absolutely necessary to avoid inefficient operation of the refrigerator after the cooling unit has become sura heavy layer of ice. This layer of ice will act as an insulator and will hinder proper transmission of cold from the cooling unit to the air within the refrigerator. The air circulation will be thereby considerably reduced and the proper preservation and cooling of food products or the like within the refrigerator cannot be ac complished without considerable loss of energy in the cooling system.

Such loss in the efiiciency of operation of mechanical refrigerators cannot be avoided, even though a great amount of attention is given to prevent the collection of a layer of ice or frost of such thickness as will interfere with an economical operation of the machine. The accumulation of the thickness of the ice crust surrounding the cooling unit is such that it is almost impossible to determine the limit of economical operation of the machine by the guess of the op- Especially in refrigerator constructions where the cooling unit is enclosed, such determination of the efliciency limits of the refrigerator is absolutely impossible. According to this, the defrosting operation will be performed at intervals, as the operator of such machine may deem necessary.

To avoid this guesswork and to determine with absolute accuracy the proper time for the defrosting operation, is the aim of the present invention, which discloses a simple and efficient indicator unit which indicates the proper time when the defrosting operation should take place.

More specifically, the invention consists of an indicator unit, preferably arranged between the front panel of the cooling unit and the cooling coil thereof. The indicator unit is provided with slidably mounted within the front panel. The extension is provided with means adapted to cooperate with the door of the refrigerator. Resilient means between the front panel and the said extension accomplish a movement of the entire indicator mechanism toward the front panel of the cooling unit when the refrigerator door is opened, while the closing of the door will return the indicator unit to its original position. This motion of the indicator is transmitted over a rod to a lever whch is adapted to perform a motion around its pivot point toward the cooling coil and to assume different positions according to the thickness of the ice 5 or frost crust on the said coil.

The variation of this ice crust on the cooling coil of the refrigerator may or may not limit the motion of this lever which in turn will impose upon the rod within the indicator unit a motion so as to thereby accomplish the operation of an ectrical switch when the economical limit of the cooling unit has been exceeded. The operation of the switch within the indicator unit will actuate signalling instrumentalities which will 15 inform the operator of the refrigerator that the efiiciency limit of the cooling system has been exceeded and the defrosting of the cooling unit must be attended to. The operation of the indicator unit is furthermore dependent upon the of the door of the refrignow closed, the defrosting indicator mechanism will be retained in its assumed position by locking instrumentalities provided therefor which are in operative engagement with the main switch which controls the operation of the motor of the entire cooling machinery. Therefore, the defrosting indicator mechanism will remain in its indicating position until the main switch for the refrigerator motor is operated to interrupt the operation of the cooling machine; and the defrosting indicator mechanism is thereby released to its original non-indicating position.

The switch within the indicator mechanism closes an electrical circuit to thereby operate any kind of signalling instrumentalities or the like which will call the attention of the attendant of the refrigerator to the fact that the defrosting operation is now to be started. 45

It will be therefore seen that the defrosting indicator will operate with great accuracy and will determine the proper time when the defrosting operation should take place and the disadvantages pointed out above will be entire- 50 1y eliminated.

A further advantage of the present construction is the cooperation between the defrosting indicator and the main switch of the motor of the refrigerator, so that the signalling instrumentalheld in place by a cotterpin ities wlil be in operation and will warn continuously the attendant of the machine, until the main switch of the refrigerator is operated and the defrosting action initiated, at which time the signalling operation of the defrosting indicator will be discontinued.

In the drawings:-

Figure 1 illustrates a partial sectional view through the cooling unit of a mechanical refrigerator, and the defrosting indicator, certain parts being shown in a diagrammatic manner.

Figure 2 is a view similar to Figure 1, showing the defrosting indicator in a position which it will assume when the refrigerator door is open.

Figure 3 is a sectional view similar to Fig. 2, indicating the operation of the indicator switch when the economical limit of the operation of the cooling unit has been exceeded, and showing the signalling means of the indicator and operation.

Figure 4 is an enlarged partial sectional view of the indicator locking instrumentalities and the cooperation of the same with the main switch of the refrigerator motor.

Figure 5 is a perspective view of a refrigerator provided with a defrosting indicator.

Figure 6 is a sectional view of the extension of the indicator housing taken along the line 6-6 of Figure 1.

Referring now to Figure l of the drawings, A illustrates the indicator housing which comprises the removable portions 13 and C which are connected to the main portion D of the housing by means of screws or the like as indicated at l. The main housing D consists of a tubular portion 2 which is adapted for the reception of a spring 3. The housing portion D is further provided with openings 4 and 5 for the reception of a rod 6 slidably arranged therein. The end portion 1 of the rod 6 is of a square configuration, and also the opening 5, so that any possible rotation of the rod 6 within the housing A is eliminated. The housing A is further provided with an extension 8 which is of a square configuration and which leads through a square opening 9 in the front panel ll! of the cooling unit. The extreme end of the extension 8 is provided with a button II and interposed between the said button and the panel I0 is a coil spring l2 which is considerably stronger than spring 3, previously described, for purposes which will be stated later on.

The square configuration of the extension 8 and the opening 9 in the front panel l0 prevents rotation of the said extension and housing A relatively to the front panel l0, so that the indicator housing is at all times retained in proper position.

Button l l of the extension 8 is adapted to abut against the door l3 of the refrigerator when the same is in closed position. When the door is opened, the housing of the indicator will be shifted with respect to the front panel In under the influence of spring i2 until the housing A abuts against the said front panel as shown in Figure 2. Closing of the door l3 will retract the extension 8 to a position as shown in Figure l and will compress the spring 12. It will therefore be obvious that whenever the door is opened and closed the above shifting of the indicator housing will take place.

The rods 6 is further provided with a washer l4 Hi. The said washer l4 forms an abutment for the spring 3 within the tubular housing D, while the other end of the coil spring 3 rests against the end wall l6 of the housing D. The rod 6 is pivotally connected at I! with the lever l8, which is turnably hinged to the frame of the cooling unit as indicated at IS. The lever I8 is furthermore provided with a contacting block which may be made from any kind of insulating material. The rod 6 is provided with a joint 2| arranged between the pivot point I! and the end wall l6 which may be of any convenient construction and adapted to permit a slight vertical motion of the end 22 of the rod 6 to prevent bending of the rod 6 when the lever I8 assumes positions as shown in Figures 2 and 3.

The housing portion B is provided with a switch 23 which comprises a switch arm 24 and control lever 25. The end of the control lever 25 is formed into the yoke .26 adapted to cooperate with collars 21 and 28 on the rod 6. The switch arm 24 is provided with a contact point 29, and a corresponding contact point 30 is mounted on the housing portion D and insulatingly spaced therefrom, as clearly shown in Figure l. The contact point 3|] is conductively connected by means of a cable 3| with a signalling circuit 32, while the switch arm 24 is conductively connected with the said signalling circuit by means of a spring 33 and a cable 34. The contact point 30 and the connections leading therefrom to the signalling circuit 32 are insulated from the housing A while such insulation of the contact 23 and switch arm 24 is not necessary and the current may travel directly over the housing to cable 34. The spring 33 may be eliminated but may be desirable to assure proper contact between the movable switch arm and the housing. Motion of the rod 6 will be transmitted by means of the collars 2'! and 28 to the control lever of the switch mechanism 35 to perform opening and closing of the signal circuit 32.

The housing portion C encloses the locking instrumentalities for the switch 23, the said locking instrumentalities comprising a latch 36 which is rotatably mounted at 31 within the said housing portion. The latch is usually held in position as shown in Figure l by means of a spring 38, and an abutment 39 integral with the housing is provided to limit the motion of the latch 36, as will be obvious from Figure 1. The housing portion C is further provided with an opening 40 through which a flexible cable 4i leads. One end of this cable is connected to the latch 36 while the other is attached to the extension 42 of the housing portion D.

A bell crank lever 43 which is mounted on a bracket 44 of the panel I0, is provided with an eyelet 45, the said eyelet entirely surrounding the cable 4| so that motion of the 43, see Figure 4, from the full line position to the dotted line position will exert a pull on the said flexible cable 4i and will move the locking member or latch 35 from the full line to the dotted line position, for purposes later on described. The bell crank lever 43 is operated incident to the operation of the main switch 46 of the electric motor of the refrigerator by means of a crank 41 attached to the pivot shaft 48 of the said switch 46. The cooperation between the bell crank lever 43 and switch 46 will be obvious from Figure 4 and need not be described in detail.

The electric circuit for the motor is indicated at 43 and the motor itself at 50. It should be noted that the entire defrosting indicator is mounted between the panel l0 nd the cooling bell crank lever I coil as shown in Figure 1, and motion of the indicator initiated by opening and closing of the door will facilitate a corresponding motion of the lever l8 so that the contacting block 20 will contact or be out of contact with the cooling coil 5|, or whatever the case may be.

In Figure 5 is a complete showing of an entire mechanical refrigerator provided with the indicator described herein and it should be noted that the main switch 46 may be located on the panel of the cooling unit or may be arranged within the outer casing of the refrigerator structure as indicated at 52. In this case it is only necessary to increase the size of the crank 41 of the switch 46 sufficiently to take care of the proper transmission of the switch operation to the lock releasing instrumentalities which are generally indicated at 53. A lamp 54 is arranged within the signalling circuit 32 and may be arranged within the casing of the refrigerator as shown in Figure 5.

The operation of the device is as follows:-

Assuming that the cooling coil of the cooling unit of the refrigerator has been defrosted and the thickness of ice surrounding it is within the limits of the economical operation of the machine-we will find that by opening of the door l3, see Figure 2, the whole indicator housing and rod 5 will be shifted from the position shown in, Figure 1 to the position of this figure under the influence of the pressure of spring l2. The lever l8 will assume a position as shown in Figure 2 and the contacting block 20 will swing toward the cooling coil 5| but will not contact with the ice collected thereon as the layer is not of sufficient thickness. The switch within the indicator housing will rema n in its position which it formerly occupied when the refrigerator door was closed and the closing of the refrigerator door will shift the entire mechanical unit to its original position shown in Figure 1. It will be seen that the cable 4| slides within the eyelet 45 of the bell crank lever 43 and the motion of the indicator housing will in no way be limited by the lock releasing instrumentalities. After a certain time of refrigeration, the cooling coil 5| will be surrounded by a layer of ice or frost which is constantly increasing as the refrigeration continues and we assume that the limit of economical operation which is relative to the thickness of the ice crust surrounding the coil has been reached. If the door is now opened, the defrosting indicator will move from the position shown in Figure 1, to the full line position shown in Figure 3, but it will be noted that the motion of the lever I8 is limited by the heavy crust of ice which is indicated at 53 and the motion of rod 6 will be stopped as soon as the contacting block 20 contacts with the ice or frost surrounding the coil 5|. As previously mentioned, the spring l2 will be considerably stronger than spring 3 and this will cause the indicator housing to be forced toward the panel H3 in the same manner as previously described, but because the rod 6 is held stationary by means of the lever l8, the contacting block of which has abutted against the layer of ice 53. the coil spring 3 will be compressed and the rod 6 will be drawn out of the indicator housing to a certain extent, or better, the housing will move with respect to the rod 6, thereby compressing the spring 3. The displacement of the rod 6 with respect to the housing A will facilitate the motion of the control lever 25 from the position shown in Figure 1 to a position shown in Figure 3 and the switch arm 24 will swing into the position shown in or looking member 36 the position shown in Figure 3 the locking member will snap back and lock the control lever of the switch in this position. The closing of the signalling circuit 32 supplies the lamp 54 with electric current and the said lamp will burn and thereby indicate that it is time to defrost the refrigerator. the door is now closed, the indicator housing, rod 6, and the lever l8 will assume the position shown in dotted lines in Figure 3, but the relation of the controlling instrumentalities for the signalling circuit 32 and the position of the looking member 36 will not be changed. The circuit remains closed and the lamp continues to burn. Any subsequent operation of the door will in no way affect the relationship of the instrumentalities arranged within the indicator housing, and the signalling means 54 will be continuously in operation until the main switch 46 is operated, which shuts off the current to the motor 50 and which thereby stops further refrigeration. As soon as the switch is operated the bell crank lever 43 will move to its dotted line position as shown in Figure 4 and the lock 36 will also move to a position as shown in dotted lines in this figure and will free the control lever 25 which will now be returned to its original position as shown in Figure 1 under the influence of spring 3 and this motion of the switch control lever will operate switch arm 24 with which it is integral and the contact points 29 and 30 are thereby separated and the signalling circuit is shut off. After a sufficient time of defrosting, the main switch 46 may be turned on again and the defrosting indicator is ready for another indicating operation.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is-

1. In a refrigerating machine having a cooling unit whereon ice is adapted to form, means for indicating when an abnormal amount of ice has accumulated, which comprises, in combination, a signal, a control for said signal, means for operating said control, which includes a pair of movable members, one of which is movable into and out of the zone of ice accumulation, said members being movable one with respect to the other when resistance in the form of ice acunit is offered to the part which is movable into the zone of ice accumulation, yieldable means for normally preventing such relative movement except under the conditions aforesaid, and means for connectparts, said last mentioned means effecting actuation of said control incident to such relative movement of the parts aforesaid.

2. In a refrigerating device having a cooling unit whereon ice forms, signal means for indicating when an abnormal amount of ice forms on said unit, which comprises. in combination, a signal, a control for operating said signal, means for operating said control, which includes a part movable into contact with said ice, a second part normally movable with said first part and additionally movable relative to said first part when ice is encountered, and means for mounting said control on said second part; said control engaging said first part and being actuated incident to relative movement between said parts. 7

3. In a refrigerating device having a cooling unit whereon ice forms, means for indicating when an abnormal amount of ice accumulates on said unit, which comprises, in combination, a signal, a control for said signal, means for operating said control, which includes a part movable into and out of contact with said ice, a second part for moving said first named part into contact with said ice, said second named part being movable with said first part and movable relative to said first named part incident to engagement of said first part with the ice, yieldable means for normally preventing such relative movement except under the conditions aforesaid, and means for mounting said control on one of said parts, said control engaging the other of said parts for actuation thereof when relative movement occurs between said parts.

4. In a refrigerating machine having a cooling unit upon which ice forms, means for indicating when an abnormal amount of ice accumulates, which comprises, in combinatio a signal, a control for said signal, means for actuating said control, which comprises a pair of movable parts, one of which is movable into engagement with the ice accumulation for limiting its movement thereby, the other of which is movable with said first named part until the ice accumulation is encountered and movable independently and relatively to said first part thereafter, yieldable means for normally preventing such relative movement except under the conditions aforesaid, means for mounting said control for movement with the second named part, means for connecting said first named part to sa'd control for actuation of said control incident to relative movement of said last named part, and resilient means for moving said last named part.

5. In a refrigerating machine having a cooling unit upon which ice forms, means for indicating when an abnormal amount of ice accumulates,

which comprises, in combination, a signal, a con-- trol for said signal, means for actuating said control, which comprises a pair of movable parts, one of w ch is movable into engagement with the ice accumulation for limiting its movement thereby, the other of which is movable with said first named part until the ice accumulation is encountered and movable independently thereafter of the first named part, means for mounting said control for movement with the second named part, means for connecting said control to said first named part for actuation of said control incident to the independent movement of said last named part, resilient means for moving said last named part, and resilient means between said parts for normally preventing independent movement as aforesaid except when ice accumulation is encountered and for restoring said first part for movement with said second part, thereby conditioning said parts for subsequent actuation of said control.

6. In a refrigerating machine having a cooling coil, means for indicating when an abnormal amount of ice has accumulated on said cooling coil, which comprises a signal, control means for operating said signal, means for operating said control, which comprises a part movable into and,

out of engagement with the ice, means for operating said first named part, including a mounting for said control movable relative to said first named part incident to movement of said first part into engagement with the ice, yieldable means for normally preventing such relative movement except under the conditions aforesaid,

means for moving said mounting and said control, means for connecting said first part with said control for actuation of said control by the relative movement aforesaid, and means for looking said control in one position of adjustment.

7. In combination with, a refrigerating machine having a cooling unit upon which ice forms, means for indicating when an excess amount of ice has so formed, which comprises, in combination, a signal, a circuit including said signal, a switch in said circuit, a switch arm, means for actuating said switch arm to open and close said circuit, said means comprising a rod having a part movable into and out of engagement with the ice accumulation on said unit, a mounting for said switch movable with said rod, and relative theretowhen said part engages the ice accumulation, yieldable means for normally preventing such relative movement except under the conditions aforesaid and for limiting the degree of movement between said mounting and said rod, and means for moving said mounting and said rod, said movement effecting bodily shifting of said mounting and switch relative to said rod when ice is encountered by said part and actuating said switch to close the circuit and energize said signal.

8. In a refrigerating machine having a cooling unit upon which ice forms, a means for indicating when an abnormal amount of ice accumulates, which comprises a signal, a control for said signal, said control having an arm, means for moving said arm to actuate said control, which comprises a rod, a member attached to said rod and movable into and out of engagement with the ice, a mounting for said control, means for connecting said mounting to said rod and for permitting relative movement between said mounting and said rod, means for connecting said arm to said rod, means for moving said mounting and said rod in one direction and forinoving said mounting independently of said rod when said member encounters an ice accumulation, said independent movement between said mounting and said rod actuating said arm, and means for preventing movement of said arm and said rod except when ice accumulation is encountered.

9. In refrigerating machine control means of the class described, in combination, a cooling unit upon which ice is adapted to form and mechanism for indicating when an abnormal amount of ice has accumulated upon said cooling unit, said mechanism including a part normally in spaced relation to the ice accumulating on the cooling unit, with means for controllably causing said part to move toward the cooling unit for contacting with the ice accumulated thereon, and operating means for said indicating mechanism operable incident to the movement of the contact part aforesaid into engagement with an abnormal amount of ice on the cooling unit.

10. In a refrigerating machine having cooling coils upon which ice is adapted to form, and a main door, means for indicating the accumulation of an abnormal amount of ice on the cooling coil, said means including a signal, a control for, said signal, means for actuatingsaid control incident to the collection of ice on said cooling coil, and means for initiating the operation of the control means, said last named means being held inoperative by the refrigerator door.

11. In a refrigerating machine having a cooling unit upon which ice is adapted to form, and the usual door, means for indicating when an abnormal amount of ice forms on the cooling unit, said means being operable incident to the opening of the refrigerator door and normally held inoperative when said door is closed, said means comprising a signal, a control for said signal, and means for actuating said control.

12. In a refrigerating machine having a cooling coil and a door, means for indicating when an abnormal amount of ice has accumulated on said cooling coil, said means being held inoperative by the door of said refrigerator when the door is in one position, said means including a signal, a control for said signal, means for actuating said control incident to the collection of ice on said cooling coil, and means for locking said control in operative position until the abnormal condition of the ice on said cooling coil has been removed.

13. In a refrigerating machine having a cooling coil and a door, means for indicating when an abnormal amount of ice has accumulated on said cooling coil, said means being held inoperative by the door of said refrigerator when the door is in one position, said means including a signal, a control for said signal, means for actuating said control incident to the collection of ice on said cooling coil, means for locking said control in operative position, and a release for said locking means.

14. In a refrigerating machine having a cooling coil and a door, means for indicating when an abnormal amount of ice has accumulated on said cooling coil, said means being held inoperative by the door of said refrigerator when the door is in one position, said means including a signal, a control for said signal, means for actuating said control incident to the collection of ice on said cooling coil, means for locking said control in operative position, and a release for said control which includes a switch operable to operate the usual motor of the cooling system.

15. In a refrigerating device including the usual cooling coil on which ice is adapted to form, means for indicating when an abnormal amount of ice has formed thereon, which comprises, a signal, a control for said signal, and means movable into and out of contact with said ice for effecting the operation of said control when an abnormal ice formation occurs.

16. In a refrigerating device including a cooling coil on which ice is adapted to form, means for indicating when an abnormal amount of ice has formed thereon, which comprises a signal, a control for said signal, means for effecting the operation of said control when an abnormal ice formation occurs, including a part movable into and out of contact with said ice, and a resilient means for moving said part into contact with said ice.

1'7. In a refrigerating device including a cooling coil on which ice forms, means for indicating when an abnormal amount of ice forms thereon, which comprises a signal, a control for said signal, means for effecting the operation of the control when an abnormal ice formation occurs, which includes instrumentalities movable into and out of engagement with the ice, instrumentalities movable relative to the movement of the first named instrumentalities when the movement of the first named instrumentalities is arrested, and means for moving both of the said instrumentalities.

18. In a refrigerator apparatus of the class described including a refrigerating chamber having a cooling coil therein and a door openable for access to said chamber, means for indicating when an abnormal amount of ice or frost forms on said cooling coil, said means comprising a signal, a control for said signal including a switch, and means for actuating said control, said last mentioned means including a casing movably mounted in said refrigerating chamber and in which said switch is mounted, a rod extending from said casing and fixed thereto, mounting means for said rod permitting longitudinal movement of said rod and said casing, said rod extending into a position engageable by the refrigerating chamber door when the door is closed second rod being slidable longitudinally in said casing and permitting relative movement between said casing and said rod incident to engagement of said member at the outer extremity of said to operate said signal when the door aforesaid is opened.

19. In a refrigerator apparatus of the class described including a refrigerating chamber having a cooling coil therein and a door openable for cooling coil, said means comprising a signal, a control for said signal including a switch, and means for actuating said control, said last mentioned means including a casing movably mountsaid rod and said casing, said rod extending into a position engageable by the refrigerating chamber door when the door is closed, means normally maintaining said rod in such door engaging position and for effecting longitudinal movement of said rod and casing when the door is opened, a second rod carried by said casing and having connection with said switch, said second rod extending outwardly from said casing and carrying at its outward extremity a, member projectable into the zone of accumulation of ice or frost on said cooling coil, said second rod being slidable longitudinally in said casing and permitting relative movement between said casing and said rod incident to engagement of said member at the outer extremity of said rod with a predetermined accumulation of ice or frost on said cooling coil, and yieldable means for normally preventing such relative movement except under the conditions aforesaid, said relative movement effecting actuation of said switch to operate said signal when the door aforesaid is opened, and lock means in said casing engageable with said switch incident to the relative movement aforesaid for maintaining actuation of said signal irrespective of further openings and closings of the door.

20. In a refrigerator apparatus of the class described including a refrigerating chamber having a cooling coil therein and a door openable for access to said chamber, means for indicating when an abnormal amount of ice or frost-forms on said cooling coil, said means comprising a signal, a control for said signal including-a switch, and means for actuating said control, said last mentioned means including a casing movably mounted in said refrigerating chamber and in which said switch is mounted, a rod extending from said casing and fixed thereto, mounting means for said rod permitting longitudinal movement of said rod and said casing, said rod extending into a position engageable by the refrigerating chamber door when the door is closed, means normally maintaining said rod in such door engaging position and for effecting longitudinal movement of said rod and casing when the door is opened, a second rod carried by said casing and having connection with said switch, said second rod extending outwardly from said casing and carrying at its outward extremity a member projectionable into the zone of accumulation of ice or frost on said cooling coil, said second rod being slidable longitudinally in said casing and permitting relative movement between said casing and said rod incident to engagement of said member at the outer extremity of said rod with a predetermined accumulation of ice or frost on said cooling coil, and yieldable means for normally preventing such relative movement except under the conditions aforesaid, said relative movement effecting actuation of said switch to operate said signal when the door aforesaid is opened, lock means in said casing engageable with said switch incident to the relative movement aforesaid for maintaining actuation of said signal irrespective of further openings and closing of the door, and manual means for releasing said lock means to restore the signal control for further actuation responsive to operation of said door.

21. In a refrigerator apparatus of the class described including a refrigerating chamber having a cooling coil therein and a door openable for access to said chamber, means for indicating when an abnormal amount of ice or frbst forms on said cooling coil, said means comprising a signal, a control for said signal including a switch, and means for actuating said control, said last mentioned means including a casing movably mounted in said refrigerating chamber and in which said switch is mounted, a rod extending.from said casing and fixed thereto, mounting means for said rod permitting longitudinal movement of said rod and said casing, said rod extending into a position engageable by the refrigerating chamber door when the door is closed, means normally maintaining said rod in such door engaging position and for effecting longitudinal movement of said rod and casing when the door is opened, a second rod carried by said casing and having connection with said switch, said second rod extending outwardly from the casing and carrying at its outward extremity a member projectionable into the zone of accumulation of ice or frost on said cooling coil, said second rod being slidable longitudinally in said casing and permitting relative movement between said casing and said rod incident to engagement of said member at the outer extremity of said rod with a predetermined accumulation of ice or frost on said cooling coil and yieldable means for normally preventing such relative movement except under the conditions aforesaid, said relative movement effecting actuation of said switch to operate said signal when the door aforesaid is opened, lock means in said casing engageable with said switch incident to the relative movement aforesaid for maintaining actuation of said signal irrespective of further openings and closings of the door, manual means for releasing said lock means to restore the signal control for further actuation responsive to operation of said door, said manual means including a flexible cable having one end connected to said lock means and the other end connected to said casing, a lever pivotally mounted in said refrigerating chamber and having slidable engagement with said cable permitting movement of said casing responsive to opening and closing of said door as aforesaid, and means for actuating said lever to apply tension to said cable and thereby trip said locking means.

JOHN J. SCHWEITZER. 

